The present invention relates generally to a vehicle speed sensor and more particularly to a vehicle speed sensor for use in a navigation or dead reckoning system.
Many vehicle navigation or route-guidance systems utilize “dead-reckoning” to propagate the position of the vehicle, usually in combination with other sensors and known techniques, such as a GPS receiver, map-matching, etc. For dead-reckoning, generally the displacement or speed of the vehicle is measured, as is the vehicle's heading. By determining the displacement of the vehicle in a determined heading, the position of the vehicle is propagated, typically relative to a database of roads.
The speed and/or displacement of the vehicle is currently obtained directly from the vehicle's electrical and control systems. Since vehicles' electrical control systems are not standardized, it is often costly or inconvenient to connect to these systems when installing a navigation system in the vehicle. Moreover, some manufacturers are eliminating the availability of speed information to “third party” electronic systems.